Refrigeration apparatus for developing extremely low temperatures

ABSTRACT

A refrigeration apparatus of the type with which gas is subjected to adiabatic expansion for the production of cold in an expansion chamber defined by a cylinder and a displacer or a piston, wherein the portions of the cylinder and displacer or piston defining the expansion chamber have complementary conical shapes and at least one of the cylinder and the displacer or the piston is arranged to function as a regenerator having a good heat transfer rate and a large specific heat.

United States Patent Sato et al. 1 Jan. 25, 1972 1 REFRIGERATION APPARATUS FOR 1 R f n Cited DEVELOPING EXTREMELY LOW UNITED STATES PATENTS TEMPERATURES 1,675,829 7/1928 Smith ..60/24 [72] Inventors: Shintlro Sato, Hachioji; Shigco Kato, 2 397 734 4/194 Goebe] Miwka, both oflapan 2,803,951 8/1957 Newton [73] Assignee: Hitachi, Ltd., Tokyo, Ja an 2,992,536 7/ i961 Carnahan ..62/6

[22] Filed: July 24, 1970 Primary Examinerwilliam J. Wye [2]] pp No; 57,954 AttorneyCraig, Antonelll, Stewart & Hill [57] ABSTRACT [30] Fem! Apphcatmnipnomy A refrigeration apparatus of the type with which gas is sub- July 29, 1969 Japan ..44/59328 jected to adiabatic expansion for the production of cold in an Nov. 14, 1969 Japan ..44/908l8 expansion chamber defined by a cylinder and a displacer or a piston, wherein the portions of the cylinder and displacer or [52] 11.8. CI ..62/6,60/24 piston defining the expansion chamber have complementary [51] lnt.Cl ..F25b 9/00 conical shapes and at least one of the cylinder and the dis- [58] placer or the piston is arranged to function as a regenerator Field of Search ..62/6; 60/24 having a good heat transfer rate and a large specific heat.

PATENTED JANZS 1972 sum 1 or 2 INVENTORS smNTaRo' 5am smcflzo KRTO -g. Wk m ATTORNEYS PATENTED JANZS i972 SHEET 2 0F 2 FIG 5 INVENTORS 8 HTC KRT' ATTORNEYS REFRIGERATION APPARATUS F OR DEVELOPING EX it YLOW TEMPERATURES BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION This invention relates to a refrigeration apparatus for developing extremely low temperatures used to liquefy gases such as helium, hydrogen or the like or to cool the instruments utilizing superconductivity, and more particularly to a refrigeration apparatus of the type which is provided with a multistage expansion chamber for effecting the adiabatic expansion of a gas.

2. DESCRIPTION OF THE PRIOR ART In the refrigeration apparatus of the described type, more stages of the expansion chamber result in a higher efficiency of refrigeration and the most ideal refrigeration apparatus will be realized by the provision of an infinite number of expansion stages. It is, however, technically impossible to provide more than three expansion stages in the conventional refrigeration apparatus as shown in FIG. 1 or 2.

The single-stage expansion displacer type refrigeration apparatus of FIG. 1 includes a gas compressor 1, a high-pressure reservoir 2 connected to the high-pressure output of the gas compressor 1, a high-pressure valve 3 connected to the highpressure reservoir 2, a cylinder 4, a displacer 5 disposed within the cylinder 4, a gas compression chamber 6 and a gas expansion chamber 7 defined in the upper and lower portions of the cylinder 4 by the displacer 5, a room-temperature seal 8 providing a herrnetical sealing between the gas compression and expansion chambers 6 and 7, a regenerator-type heat exchanger 9 provided between the gas compression and expansion chambers 6 and 7, a low-pressure valve 10, a lowpressure reservoir 11 connected to the low-pressure valve 10, a conduit 12 connecting the gas compression chamber 6 to the high-pressure valve 3 and to the low-pressure valve 11, a crank mechanism 13 for imparting reciprocal movement to the displacer 8, and a motor 14 for driving the crank mechanism 13.

In operation, gases such as helium, hydrogen or the like compressed by the compressor 1 have their pressure regulated by the high-pressure reservoir 2. n the other hand, the displacer is imparted a reciprocal movement by the crank mechanism 13 driven from the motor 14. The high-pressure valve 3 and the low-pressure valve are operated in synchronism with the movement of the displacer 5. In other words, when the displacer 5 is at the lower dead point the high-pressure valve 3 is opened to admit the compressed gas into the compression chamber 6 within the cylinder 4. (The low-pressure valve 10 is closed at that time.) When the displacer 5 starts to move up, the gas within the compression chamber 6 is compressed and then passes through the regenerator-type heat exchanger 9, where the gas exchanges heat with it, and is then supplied to the expansion chamber 7. Any insufiicient supply of the gas is compensated for by the high-pressure reservoir 2. When the displacer 5 reaches the upper dead point, the high-pressure valve 3 is closed and the low-pressure valve 10 is simultaneously opened. As a result, the gas in the expansion chamber 7 effects adiabatic expansion and thereby the gas decreases its temperature and produces cold. When the displacer 5 starts to move down, the gas in'the expansion chamber 7 passes through the regenerator-type heat exchanger 9 where the gas exchanges-heat with it and gives it cold, and then the gas is returned to the low-pressure input of the compressor 1 via compression chamber 6, low-pressure valve 10 and low-pressure reservoir 11. When the displacer 5 reaches the lower dead point again, the lciwpressure valve 10 is closed and the high-pressure valve 3 is opened, thus completing one cycle of refrigeration. Such a cycle is repeated to cool the gas to extremely low temperatures.

It il now assumed that the room temperature is T. and that refrigeration ofhest Q; is to be effected at a temperature 'I, by the use of the above-described refrigeration apparatus. All the temperatures mentioned hereln are absolute temperatures.

Because of the essential nature of the refrigeration apparatus, it is always the case that when refrigeration is effected at the temperature T there is a heat input from outside at this or a higher temperature. It is assumed that the heat input is Q, for a temperature T; and Q, for a temperature Tg. In the above-described single-stage expansion-type refrigeration apparatus'which has a single expansion chamber producing cold, the heat input is reduced from T and T, to T, even if T, and T, are higher than T Thus, the work L required for refrigeration may be expressed as:

L. T.{ 3%+A.% +1s%} (1) wherein A represents a coefiicient corresponding to the temperature I and expressing the increase of work resulting from the difference between the working gas and an ideal gas, the irreversible process and the dead space of the refrigeration apparatus, and the value of A is greater than 1. Therefore, in such a single-stage expansion-type refrigeration apparatus having only one expansion chamber, all the heat inputs are reduced to the temperature 1 which produces cold, and it is apparent from equation (I) that a large amount of work is required to achieve refrigeration at an extremely low temperature, i.e., at T of small value.

Another known refrigeration apparatus is of the three-stage expansion type which has been developed from the singlestage expansion type of FIG. 1 so that expansion is effected at temperatures T T and T to produce cold.

Such a three-stage expansion-type refrigeration apparatus of the prior art is shown in FIG. 2. The apparatus of FIG. 2 differs from that of FIG. 1 in that, as shown, cylinder 4 and displacer 5 are respectively formed by three continuous cylinders and pillars of different diameters, that in accordance with the movement of the displacer 5 the gas is expanded in three expansion chambers, i.e., first, second and third expansion chambers 7a, 7b and 7c so as to produce cold, and that three regenerator, i.e., first, second and third heat exchangers 9a, 9b and 9:: correspond to the three expansion chambers 7a, 7b and 70, respectively.

When there are heat inputs Q and Q, at temperatures T and T respectively and when refrigeration of heat 0;, is to be effected at a temperature T the work L required for this three-stage expansion-type refrigeration apparatus may be expressed as:

When the relations expressed by equations (3) and (4) are taken into account, it will be apparent that L of equation (2) is smaller than I.. of equation l It will thus be appreciated that the refrigeration apparatus of the three-stage expansion type is far more efiicient than that of the single-stage expansion type and can accomplish a higher degree of refrigeration at a lower temperature for an equal amount of given work.

Actually, however, the temperatures at which heat input takes place are not limited to the two described temperature levels but heat input can take place at infinite temperature levels or heat to be absorbed is present infinitely. Therefore, in an actual refrigeration apparatus, more stages of expansion may result in a higher efficiency and the most ideal refrigeration apparatus will be one which has an infinite number of expansion stages.

However, this is technically difficult and three stages has been the greatest possible number of expansion stages according to the prior art. Furthennore, in case of a refrigeration appnratun having two or more expansion stages, seals (as indlcated at 8!: and 8c in FIG. 2) provided to prevent the gun from short-circuiting between expansion chambers without passing through the regenerator-type heat exchangers are in low-temperature ranges, with unfavorable results that heat is produced by the friction of these seals or the gas leaks through the seals, which means a wasteful consumption of the cold produced in the expansion chambers.

The foregoing discussion, which has been directed to the displacer-type refrigeration apparatus, also holds true with the piston type or the inverse Stirlings type refrigeration apparatus, the latter type utilizing a combination of the displacer type and the piston type. This will become more apparent from the following detailed description of the present invention.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved refrigeration apparatus for developing extremely low temperatures with high efficiency.

It is another object of the present invention to provide a simply constructed refrigeration apparatus having a number of expansion stages which may be called the infinite expansion stage type.

It is still another object of the present invention to provide a refrigeration apparatus using no low-temperature seal which may result in gas leakage or friction heat. These and other objects and advantages and features of the present invention will become fully apparent from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic illustration of the single-stage expansion-type refrigeration apparatus using a displacer according to the prior art.

FIG. 2 is a diagrammatic illustration of the three-stage expansion-type refrigeration apparatus using a displacer according to the prior art.

FIG. 3 is a diagrammatic illustration of the displacer-type refrigeration apparatus according to an embodiment of the present invention.

FIG. 4 is a model illustration for showing the manner in which cold is produced in the expansion chamber of the apparatus shown in FIG. 3.

FIG. 5 is a diagrammatic illustration of the piston-type refrigeration apparatus according to another embodiment of the present invention.

FIG. 6 is a diagrammatic illustration of the inverse Stirlings type refrigeration apparatus according to still another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout FIGS. 3 to 6 showing the various embodiments of the present invention, parts similar to those of FIGS. 1 and 2 are indicated by like reference characters.

Referring to FIG. 3, an example of the displacer-type refrigeration apparatus embodying the present invention includes a cylinder 4 having a conically shaped lower portion, and a displacer 5 having a complementary lower portion. Heat exchangers l5 and 16 having a good heat transfer rate and a large specific heat are provided outside or inside the opposed conical surfaces of the cylinder 4 and displacer 5. The heat exchangers l5 and 16 may be formed as by wires of copper, copper alloy or like metal close-coiled into a layer, by screens of such metal turned into a layer or by balls or perforated disks of such metal.

In operation, the gas compressed by the compressor 1 has its pressure regulated by the high-pressure reservoir 2. On the other hand, the displacer 5 is driven for reciprocal movement from the motor 14 through the crank mechanism 13. The high-pressure valve 3 and low-pressure valve are operated in synchronism with the displacer 5. In other words, when the displacer 5 is at the lower dead point the high-pressure valve 3 is opened to admit the compressed gas into the compression chamber 6 within the cylinder 4. (The low-pressure valve 10 is closed at that time.) When the displacer 5 starts to move up, the gas within the compression chamber 6 passes through the regenerator-type heat exchanger 9, where the gas exchanges heat, and is then supplied into the expansion chamber 7. The expansion chamber 7 is a very narrow, annular, conical clearance defined by the regenerator-type heat exchangers l5 and 16, and therefore the gas introduced thereinto completely exchanges heat with these regenerator-type heat exchangers l5 and 16 while it reaches the top of the displacer 5. When the displacer 5 reaches the upper dead point, the high-pressure valve 3 is closed and the low-pressure valve 10 is opened at the same time. The gas within the expansion chamber 7 effects adiabatic expansion everywhere in that chamber and thereby produces cold. Subsequently, when the displacer 5 starts to move down, the cold gas within the expansion chamber 7 exchanges heat with the regenerator-type heat exchangers 15 and 16 while moving in that chamber, whereafier the gas further exchanges heat with the regenerator-type heat exchanger 9 and passes through the compression chamber 6, low-pressure valve 10 and low-pressure reservoir 11 into the compressor 1 1 again. Thereafter, when the displacer 5 returns to the lower dead point, the low-pressure valve 10 is closed and the high-pressure valve 3 is opened, thereby completing one cycle of refrigeration. Such a cycle is then repeated so that the expansion chamber 7 is cooled down to extremely low temperatures while keeping a temperature gradient in the lengthwise direction thereof.

If the vertical angle of each of the cones formed by the cylinder 4 and displacer 5 of the above-described refrigeration apparatus is 20 and the axial length thereof is I, then the volume variation dV in the expansion chamber 7 for a fine displacement dh of the displacer 5 from the apex to a height h will be expressed as:

(W =21rtan6-l-ah (5 This means that the volume variation dV in the expansion chamber 7 is in proportion to the height h from the apex and accordingly that the volume variation is greater with the distance from the apex.

Furthermore, the portions of the cylinder 4 and displacer 5 which provide the conically shaped regenerator-type heat exchangers are closely spaced apart from each other but have great axial dimensions, so that parts of the gas which are most slightly spaced apart axially of the expansion chamber 7 therewithin are thermally separated from each other by the regenerator-type heat exchangers. In other words, the expansion chamber 7 is thermally divided into numerous separate portions by numerous regenerator-type heat exchangers.

FIG. 4 is a model illustration for the better understanding of the cold producing portion in the refrigeration apparatus of the present invention. As shown, the compression chamber 6 is connected on the one hand to the system of the compressor 1 (not shown) and on the other hand to the regenerator-type heat exchanger 9. Below the regenerator-type heat exchanger 9, there is a portion of the expansion chamber 7, which in turn is followed by portions of the regenerator-type heat exchangers 16 and 15 arranged in pairs with portions of the expansion chamber 7 interposed therebetween. Such arrangement continues almost infinitely toward the apex of the cone. Thus, according to the present invention, the refrigeration apparatus is provided with numerous expansion stages each of which comprises one expansion chamber and one regenerator-type heat exchanger.

Thus, the present invention can provide a refrigeration apparatus which has numberless expansion stages and which is thermodynamically highly eflicient. Further, this refrigeration apparatus is of such a construction that gas passes through the clearance defined between the cylinder and the displacer and is surrounded by regenerator-type heat exchangers which also provide innumerable expansion chamber portions, and such a construction can eliminate the low-temperature seals as seals 8b and 8c of FIG. 2 which have heretofore been used to divide the expansion chamber into a number of stages in the prior art. This in turn results in the elimination of the wasteful consumption of the cold which would otherwise be induced by the friction heat of such seals and gas leakage through the seals, whereby there is provided a great industrial advantage including an increased capacity of refrigeration and so forth.

In the above-described embodiment of the present invention, it will be readily appreciated that one of the regeneratortype heat exchangers l5 and 16 may be omitted if desired.

Referring to FIG. 5, there is shown the piston-type refrigeration apparatus according to another embodiment of the present invention. In this alternative form of the invention, the gas compressed by the compressor 1 has its pressure regulated by the high-pressure reservoir 1. When the piston 5 is at the lower dead point, the high-pressure valve 3 is opened to admit the gas through the regenerator-type heat exchanger 9 into the cylinder 4, where the gas exchanges heat with the regeneratortype heat exchangers 15 and 16 while passing into the expansion chamber 7. When the piston 5 starts to move up, the lowpressure valve is closed so that the gas everywhere in the expansion chamber 7 effects adiabatic expansion to thereby produce cold. The work carried out by the gas with respect to the piston is absorbed by a brake 18 attached to the crank mechanism 13 connected to the piston 5. When the piston 5 reaches the upper dead point, the low-pressure valve 10 is opened and then the piston starts to move down. The cold gas within the expansion chamber 7 exchanges heat with the regenerator-type heat exchangers l5 and 16 and further with the regenerator-type heat exchanger 9, and thereafter passes through the low-pressure valve 10 and low-pressure reservoir 11 into the compressor 1 again. Thus, one cycle of refrigeration has been completed. Such a cycle is then repeated to cool the expansion chamber 7.

The expansion chamber 7 of this apparatus is entirely the same in construction as that of FIG. 3, and accordingly the same in the principle and efi'ect of refrigeration.

Referring to FIG. 6, there is shown a further example of the present invention which takes the form of the inverse stirlings type refrigeration apparatus. As shown, the apparatus is driven from the motor 14. The drive from the motor is transmitted to a crank 19, which in turn drives a compression piston '20 and an expansion piston 5. The expansion piston 5 is about 90 ahead in phase with respect to the compression piston 20. Because of such phase difference between the two pistons, the gas within a compression chamber 21 is compressed when the compression piston 20 moves up, and the compressed gas is deprived of compression heat by a cooler 22 and cooled to the room temperature, whereafter the passes through the regenerator-type heat exchanger 9 into the expansion chamber 7, which is entirely of the same construction as that of FIG. 3. The gas admitted into the expansion chamber 7 exchanges heat with the regenerator-type heat exchangers l5 and 16 while moving toward farthest end or top of the conical expansion chamber 7. When the crank 19 is rotated to lower the expansion piston 5, the gas everywhere in the expansion chamber 7 effects adiabatic expansion to thereby produce cold. As the crank is further rotated, the cold gas in the expansion chamber 7 is forced out by the lifting expansion piston 5, whereupon the gas well exchanges heat with the regenerator-type heat exchangers l5 and 16. Thereafter the gas cools the regenerator-type heat exchanger 9 and returns to the compression chamber 21. By that time, the compression piston 20 has already reached the lower dead point. Thus, one cycle of refrigeration has been completed, and such cycle is repeated so that the expansion chamber 7 reaches extremely low temperatures while keeping a temperature gradient in the axial direction thereof.

The embodiment of FIG. 6 has entirely the same expansion chamber 7 and accordingly the same refrigeration mechanism and effect as the embodiments of FIGS. 3 and 5.

It will thus be appreciated that the present invention provides a novel refrigeration apparatus of very high efficiencg'.

While various embodiments of the present invention ave been shown and described above, the present invention is in no way limited to such specific embodiments and many changes and modification may be made therein without departing from the spirit of the present invention.

We claim:

1. An expansion-type refrigeration apparatus comprising a cylinder, a movable displacer disposed within said cylinder so as to define a compression chamber and an expansion chamber by cooperation with said cylinder, a regenerator-type heat exchanger connected between said compression chamber and said expansion chamber, drive means for imparting reciprocal movement to said displacer, compressor, a highpressure reservoir and a low-pressure reservoir connected to the high-pressure output and the low-pressure input of said compressor respectively, and a low-pressure valve and a highpressure valve provided with means for communicating said low-pressure and high-pressure reservoirs with said compression chamber when said displacer is positioned at the upper and lower dead points thereof, respectively, wherein the portions of said cylinder and said displacer which define said expansion chamber have conical shapes complementary to each other, and at least one of said conical portions of said cylinder and said movable member has the construction of a regenerator-type heat exchanger having a good heat transfer rate and a large specific heat.

2. An expansion-type refrigeration apparatus comprising a cylinder, a movable piston disposed within said cylinder so as to define an expansion chamber by cooperation with said cylinder, a regenerator-typeheat exchanger connected to said expansion chamber, a compressor, a high-pressure reservoir and a low-pressure reservoir connected the high-pressure output and the low-pressure input of said compressor respectively, a low-pressure valve and a high-pressure valve provided with means for communicating said low-pressure and highpressure reservoirs with said expansion chamber when said piston is at the upper and lower dead points thereof, respectively, and means for absorbing the work effected with respect to said piston by said high-pressure gas, wherein the portions of said cylinder and said piston which define said expansion chamber have conical shapes complementary to each other, and at least one of said conical portions of said cylinder and said piston has the construction of a regenerator-type heat exchanger having a good heat transfer rate and a large specific heat.

3. An expansion-type refrigeration apparatus comprising a cylinder, a movable expansion piston disposed within said cylinder so as to define an expansion chamber by cooperation with said cylinder, a regenerator-type heat exchanger connected to said expansion chamber at one side thereof, a compressor having a cylinder and a compression piston wherein said cylinder is connected with the other side of said regenerator-type heat exchanger, a gas cooler provided between said heat exchanger and said compressor, and means for driving said expansion piston and said compression piston with a phase difference of approximately therebetween, wherein the portions of said cylinder and said expansion piston which define said expansion chamber have conical shapes complementary to each other, and at least one of said conical portions of said cylinder and said expansion piston has the construction of a regenerator-type heat exchanger having a good heat transfer rate and a large specific heat. 

1. An expansion-type refrigeration apparatus comprising a cylinder, a movable displacer disposed within said cylinder so as to define a compression chamber and an expansion chamber by cooperation with said cylinder, a regenerator-type heat exchanger connected between said compression chamber and said expansion chamber, drive means for imparting reciprocal movement to said displacer, compressor, a high-pressure reservoir and a lowpressure reservoir connected to the high-pressure output and the low-pressure input of said compressor respectively, and a lowpressure valve and a high-pressure valve provided with means for communicating said low-pressure and high-pressure reservoirs with said compression chamber when said displacer is positioned at the upper and lower dead points thereof, respectively, wherein the portions of said cylinder and said displacer which define said expansion chamber have conical shapes complementary to each other, and at least one of said conical portions of said cylinder and said movable member has the construction of a regeneratortype heat exchanger having a good heat transfer rate and a large specific heat.
 2. An expansion-type refrigeration apparatus comprising a cylinder, a movable piston disposed within said cylinder so as to define an expansion chamber by cooperation with said cylinder, a regenerator-type heat exchanger connected to said expansion chamber, a compressor, a high-pressure reservoir and a low-pressure reservoir connected the high-pressure output and the low-pressure input of said compressor respectively, a low-pressure valve and a high-pressure valve provided with means for communicating said low-pressure and high-pressure reservoirs with said expansion chamber when said piston is at the upper and lower dead points thereof, respectively, and means for absorbing the work effected with respect to said piston by said high-pressure gas, wherein the portions of said cylinDer and said piston which define said expansion chamber have conical shapes complementary to each other, and at least one of said conical portions of said cylinder and said piston has the construction of a regenerator-type heat exchanger having a good heat transfer rate and a large specific heat.
 3. An expansion-type refrigeration apparatus comprising a cylinder, a movable expansion piston disposed within said cylinder so as to define an expansion chamber by cooperation with said cylinder, a regenerator-type heat exchanger connected to said expansion chamber at one side thereof, a compressor having a cylinder and a compression piston wherein said cylinder is connected with the other side of said regenerator-type heat exchanger, a gas cooler provided between said heat exchanger and said compressor, and means for driving said expansion piston and said compression piston with a phase difference of approximately 90* therebetween, wherein the portions of said cylinder and said expansion piston which define said expansion chamber have conical shapes complementary to each other, and at least one of said conical portions of said cylinder and said expansion piston has the construction of a regenerator-type heat exchanger having a good heat transfer rate and a large specific heat. 